Electrocardiographic QT interval and mortality: a meta-analysis

Antipsychotic Polypharmacy and Corrected QT Interval: A Systematic Review

OBJECTIVE

It remains unclear whether antipsychotic polypharmacy, a common clinical practice, is related to an increased risk of corrected time between start of Q wave and end of T wave (QTc) interval prolongation. We conducted a systematic review of the literature to address this important issue.

METHOD

A systematic literature search was conducted in October 2014, using MEDLINE, Embase, and PsycINFO. Studies and case reports were included if they reported QTc intervals or QTc interval changes before and after antipsychotic polypharmacy or QTc intervals in both antipsychotic polypharmacy and monotherapy groups.

RESULTS

A total of 21 articles (10 clinical trials, 4 observational studies, and 7 case reports) met inclusion criteria. The clinical trials have shown that a combination treatment with risperidone or pimozide is not obviously related to an increase in QTc interval, whereas ziprasidone or sertindole combined with clozapine may prolong QTc interval. Among the 4 observational studies, antipsychotic polypharmacy was not clearly associated with QTc prolongation in 3 studies, each cross-sectional. In contrast, one prospective study showed a significant increase in QTc interval following antipsychotic coadministration. The case reports indicated an increased risk of QTc prolongation in at least some patients receiving antipsychotic polypharmacy.

CONCLUSIONS

Currently available evidence fails to confirm that antipsychotic polypharmacy worsens QTc prolongation in general, although the evidence is scarce and inconsistent. Clinicians are advised to remain conservative in resorting to antipsychotic polypharmacy, as a combination of some QTc-prolongation liable antipsychotics may further prolong QTc interval, and efficacy supporting the clinical benefits of antipsychotic polypharmacy is equivocal, at best.

QT interval variations and mortality risk: is there any relationship?

Abnormal prolongation and shortening of the electrocardiographic QT interval duration, which occur in the hereditary forms of long and short QT syndromes, are associated with an increased risk of ventricular arrhythmias and sudden cardiac death. Even within the normal range, these altered durations are associated with an increased mortality risk in the general population. While extreme prolongation or reduction of the QT interval predisposes patients to malignant ventricular arrhythmias and sudden cardiac death, the precise dose-response relationship between the QT interval and cardiovascular disease mortality is still unknown. This paper describes the need for more standardized methods for measuring and reporting the QT interval and the need for more precise assessments of the risk associated with QT interval variation.

Association between corrected QT interval and inflammatory cytokines in rheumatoid arthritis

OBJECTIVE

Corrected QT (QTc) interval predicts all-cause and cardiovascular mortality and may contribute to the increased mortality risk in rheumatoid arthritis (RA). Animal experiments have shown that proinflammatory cytokines [tumor necrosis factor (TNF)-α and interleukin 1 (IL-1)] can prolong cardiomyocyte action potential. We sought to determine whether elevations in circulating inflammatory cytokines were independently associated with QTc prolongation in patients with RA.

METHODS

One hundred twelve patients [median age 62 (interquartile range 17) yrs; 80 women (71%)] from a well-characterized RA cohort underwent baseline 12-lead electrocardiograms for QT interval measurement and contemporary blood sampling to assess concentrations of inflammatory markers including C-reactive protein (CRP), TNF-α, and interleukins (IL-1α, IL-1β, IL-6, IL-10). QTc was calculated using the Bazett (QTBAZ = QT ÷ √RR) and Framingham Heart Study (QTFHS = QT + 0.154 × [1 - RR]) heart rate correction formulas.

RESULTS

Inflammatory cytokines (TNF-α, IL-1β, IL-6, IL-10) were positively correlated with QTBAZ (Spearman rank correlation coefficient rho = 0.199, 0.210, 0.222, 0.333; all p < 0.05). In multivariable regression analysis, these associations were all confounded by age except IL-10, where higher tertile groups were independently and positively associated with QTBAZ (β = 0.202, p = 0.023) and QTFHS (β = 0.223, p = 0.009) when compared to the lower tertile. CRP (per unit increase) was independently associated with QTBAZ (β = 0.278, p = 0.001), but not QTFHS.

CONCLUSION

To our knowledge, ours is the first study demonstrating a contemporary link between inflammatory cytokines and QT interval in humans. Our results suggest that a lower inflammatory burden may protect against QTc prolongation in patients with RA. However, further studies are required to confirm the effects of pro- and antiinflammatory cytokines on QTc interval.

Prolonged QTc Interval Predicts Poststroke Paroxysmal Atrial Fibrillation

Background and Purpose—

Paroxysmal atrial fibrillation (PAF) is often difficult to detect in patients with acute ischemic stroke. We aimed to assess the predictive value of a prolonged QT interval corrected for heart rate (QTc) in PAF detection after acute ischemic stroke.

Methods—

We enrolled 972 patients with acute ischemic stroke consecutively extracted from our observational stroke registry system. Exclusion criteria were as follows: (1) AF on the initial 12-lead ECG (n=171); (2) previously diagnosed PAF (n=47); and (3) the use of a cardiac pacemaker (n=10). Of the 972 patients, 744 (mean age, 67.6 years; men, 62.6%) were eligible for analysis. The clinical characteristics and 12-lead ECG findings of the patients with and without PAF were compared, and multiple logistic regression analysis was performed to identify predictors of poststroke PAF.

Results—

The poststroke cardiac work-up yielded 69 (9.3%) de novo PAF cases among the 744 patients. The QTc interval was significantly longer in patients with PAF than in those without PAF (436 versus 417 ms; P <0.001). Each 10-ms increase in the QTc interval was associated with an increased risk of PAF after multivariate adjustments (odds ratio, 1.41; 95% confidence interval, 1.24–1.61; P <0.001). The optimal threshold value of QTc interval calculated by a receiver-operating characteristic curve was 438 ms, and the area under the curve was 0.73 in this data set.

Conclusions—

The QTc interval prolongation is potentially a strong and useful predictor for poststroke PAF.

Population-based study of QT interval prolongation in patients with rheumatoid arthritis

OBJECTIVES

Patients with rheumatoid arthritis (RA) are at increased risk of cardiovascular morbidity and mortality. Heart rate corrected QT interval (QTc) (which is obtained from a 12-lead electrocardiogram (ECG) and reflects ventricular repolarisation duration) is a strong predictor of cardiovascular mortality. Our primary purpose is to determine the impact of QTc prolongation on mortality in RA patients.

METHODS

A population-based inception cohort of patients with RA fulfilling the 1987 ACR criteria in 1988-2007 was identified, with an age- and sex-matched comparison cohort and followed until death, migration or until the end of 2008. Data were collected on ECG variables, medications known to prolong QT interval, electrolytes, cardiovascular risk factors and disease status and RA disease characteristics. Cox proportional hazards models were used to examine QTc prolongation as predictor of mortality.

RESULTS

QTc prolongation prior to RA incidence/index date was similar in RA (15%) and non-RA (18%) subjects. During follow-up, the cumulative incidence of QTc prolongation was higher among RA (48% at 20 years after RA incidence) than non-RA (38% at 20 years after index date; p=0.004). Idiopathic QTc prolongation (excluding prolongations explained by ECG changes, medications, etc.) was marginally associated with all-cause mortality (HR: 1.28; 95% CI: 0.91-1.81, p=0.16), but was not associated with cardiovascular mortality (HR: 1.10; 95% CI:0.43-2.86, p=0.83) in RA.

CONCLUSIONS

RA patients have a significantly elevated risk of developing QTc prolongation. However, idiopathic prolonged QTc was only marginally associated with all-cause mortality in RA patients. The clinical implications of these findings in RA require further study.

The genetics of pro-arrhythmic adverse drug reactions

Ventricular arrhythmia induced by drugs (pro-arrythmia) is an uncommon event, whose occurrence is unpredictable but potentially fatal. The ability of a variety of medications to induce these arrhythmias is a significant problem facing the pharmaceutical industry. Genetic variants have been shown to play a role in adverse events and are also known to influence an individual's optimal drug dose. This review provides an overview of the current understanding of the role of genetic variants in modulating the risk of drug induced arrhythmias.

The QT interval is associated with incident cardiovascular events: the MESA study

BACKGROUND

Prolonged heart rate-corrected QT interval on electrocardiograms (ECGs) is associated with increased risk of myocardial infarction and cardiovascular disease (CVD)-related deaths in patients with prevalent coronary heart disease.

OBJECTIVES

This study sought to examine the prognostic association between the baseline QT interval and incident cardiovascular events in individuals without prior known CVD.

METHODS

The corrected baseline 12-lead ECG QT interval duration (QTcorr) was determined by adjustment for age, sex, race/ethnicity, and RR interval duration in 6,273 participants in MESA (Multi-Ethnic Study of Atherosclerosis). Cox proportional hazards models adjusting for demographic and clinical risk factors were used to examine the association of baseline QTcorr with incident cardiovascular events.

RESULTS

The mean age at enrollment was 61.7 ± 10 years, and 53.4% of participants were women. Cardiovascular events occurred in 291 participants over a mean follow-up of 8.0 ± 1.7 years. Each 10-ms increase in the baseline QTcorr was associated with incident heart failure (hazard ratio [HR]: 1.25; 95% CI: 1.14 to 1.37), CVD events (HR: 1.12; 95% CI: 1.05 to 1.20), and stroke (HR: 1.19; 95% CI: 1.07 to 1.32) after adjustment for CVD risk factors and potential confounders. There was no evidence of interaction with sex or ethnicity.

CONCLUSIONS

The QT interval was associated with incident cardiovascular events in middle-aged and older adults without prior CVD.

Evidence of heterogeneity by race/ethnicity in genetic determinants of QT interval

BACKGROUND

QT interval (QT) prolongation is an established risk factor for ventricular tachyarrhythmia and sudden cardiac death. Previous genome-wide association studies in populations of the European descent have identified multiple genetic loci that influence QT, but few have examined these loci in ethnically diverse populations.

METHODS

Here, we examine the direction, magnitude, and precision of effect sizes for 21 previously reported SNPs from 12 QT loci, in populations of European (n = 16,398), African (n = 5,437), American Indian (n = 5,032), Hispanic (n = 1,143), and Asian (n = 932) descent as part of the Population Architecture using Genomics and Epidemiology (PAGE) study. Estimates obtained from linear regression models stratified by race/ethnicity were combined using inverse-variance weighted meta-analysis. Heterogeneity was evaluated using Cochran's Q test.

RESULTS

Of 21 SNPs, 7 showed consistent direction of effect across all 5 populations, and an additional 9 had estimated effects that were consistent across 4 populations. Despite consistent direction of effect, 9 of 16 SNPs had evidence (P < 0.05) of heterogeneity by race/ethnicity. For these 9 SNPs, linkage disequilibrium plots often indicated substantial variation in linkage disequilibrium patterns among the various racial/ethnic groups, as well as possible allelic heterogeneity.

CONCLUSIONS

These results emphasize the importance of analyzing racial/ethnic groups separately in genetic studies. Furthermore, they underscore the possible utility of trans-ethnic studies to pinpoint underlying casual variants influencing heritable traits such as QT.

Managing cardiovascular disease risk in patients treated with antipsychotics: a multidisciplinary approach

Background

The use of antipsychotic medication in the United States and throughout the world has greatly increased over the last fifteen years. These drugs have significant side effect burdens, many of them relating to cardiovascular health.

Objective

To review the available evidence on the major cardiovascular issues that arise in patients taking antipsychotic medication.

Method

A PubMed literature review was performed to identify recent meta-analyses, review articles, and large studies. Further articles were identified through cited papers and based on expert consultation when necessary.

Results

Clinical guidance on the following adverse effects and antipsychotics was reviewed: electrocardiogram (ECG) changes, (specifically, prolonged QT and risk of torsades de pointes), weight gain, dyslipidemia, metabolic syndrome, and myocarditis. Specific attention was paid to monitoring guidelines and treatment options in the event of adverse events, including dose change, medication switch, or adjuvant therapy.

Impact of clinical decision support preventing the use of QT-prolonging medications for patients at risk for torsade de pointes

We developed and implemented a 'CPOE-QT Alert' system, that is, clinical decision support integrated in the computerized physician order entry system (CPOE), in 2011. The system identifies any attempts to order medications with risk of torsade de pointes (TdP) for patients with a history of significant QT prolongation (QTc ≥500 ms) and alerts the provider entering the order. We assessed its impact by comparing orders and subsequent medication administration before and after activation of the system. We found a significant decrease in the proportion of completed order per ordering attempt after system activation (94% (1293/1379) vs 77% (1888/2453), difference 16.8%; p<0.001). This resulted in a 13.9% reduction in the administration of those medications to patients. A significant decrease was observed across all provider types, educational levels, and specialties. The CPOE-QT Alert system successfully reduced exposure to QT-prolonging medications in high risk patients.

Comparison of study designs used to detect and characterize pharmacogenomic interactions in nonexperimental studies: a simulation study

OBJECTIVES

Adverse drug reactions are common, serious, difficult to predict, and may be influenced by genetics, prompting the increasing popularity of pharmacogenomic studies. Many pharmacogenomic studies are conducted in nonexperimental settings, yet little is known about the influence of confounding by contraindication. We, therefore, compared the two designs [the overall population (OPD) and the treated-only (TOD) design] by simulating a pharmacogenomic study of the ECG QT interval (QT).

METHODS

Simulations were informed by data from the Atherosclerosis Risk in Communities Study and a literature review examining QT, QT-prolonging drug use, and modification by single nucleotide polymorphisms (SNP). Drug treatment was assigned on the basis of age, sex, and QTlong, representing confounding by contraindication. QT was simulated as a function of drug treatment, one SNP, the drug-SNP interaction, and clinical covariates.

RESULTS

Failure to adjust for confounding by contraindication produced a varying degree of bias in the OPD, whereas the TOD was biased by the SNP main effect. For example, in the OPD, the false-positive proportion for the drug-SNP interaction was 5% across the range of SNP main effects (0-10 ms), but increased to 19% without adjusting for confounding by contraindication. In the TOD, the false-positive proportion increased to 89% with SNP main effects greater than 4 ms, although bias was reduced by 39% with adjustment for covariates affected by the SNP.

CONCLUSION

The potential for bias from confounding by contraindication (OPD) should be weighed against bias from SNP main effects (TOD) when selecting the study design that best suits the given context.

Risk factors for QT prolongation associated with acute psychotropic drug overdose

BACKGROUND

Antipsychotic/Antidepressant use is a risk factor for QT interval (QT) prolongation and sudden cardiac death. However, it is unclear which drugs are risk factors for QT prolongation and torsades de pointes in cases of psychotropic drug overdose.

METHODS

After correction of QT data by Bazett formula (QTc), QTc was classified into 3 categories (QTc<440 milliseconds, 440 milliseconds≤QTc<500 milliseconds, and QTc≥500 milliseconds), and the blood concentration of each drug was classified as not detected, therapeutic range, or toxic range. The association of the blood concentration of each drug with QTc was analyzed using the ordinal logistic regression model. Drugs that induced QT-heart rate pairs higher than the at-risk line of Isbister's QT-heart rate nomogram (QT nomogram) were further analyzed using the binomial logistic regression model.

RESULTS

A total of 649 patients were enrolled in the study. The independent risk factors for QTc prolongation were therapeutic and toxic range of phenotiazine antipsychotic drug (therapeutic range: odds ratio [OR], 1.56 [P=.039]; toxic range: OR, 3.85 [P<.001]), and toxic range of cyclic antidepressants (OR, 2.39; P=.018). In addition, toxic range of phenotiazine antipsychotic drug (OR, 3.87; P=.012) and tricyclic antidepressants (OR, 4.94; P<.001) were risk factors for QT higher than the at-risk line of the QT nomogram.

CONCLUSIONS

The possibility of QT prolongation and torsades de pointes due to overdose of phenotiazine antipsychotic drug or tricyclic antidepressants requires particular consideration.

Does glycemic control reverse dispersion of ventricular repolarization in type 2 diabetes?

Background

Abnormal ventricular repolarization is a predictor of cardiovascular mortality. In this study, we tested the hypothesis that glycemic control reverses abnormal ventricular repolarization in patients with type 2 diabetes.

Methods

We analyzed longitudinal changes in repolarization indices of electrocardiograms in retrospectively enrolled 44 patients with type 2 diabetes and 44 age-matched healthy subjects.

Results

In the diabetic group, BMI was greater, levels of HbA1c (10.0 ± 1.6 vs. 5.6 ± 0.3%) and triglyceride were higher and level of HDL cholesterol was lower than those in the control group. Although mean QTc intervals were similar (413.6 ± 18.5 vs. 408.3 ± 22.7 ms), QT dispersion (41.8 ± 15.4 vs. 28.7 ± 7.7 ms) and Tpeak-Tend in lead V5 (83.6 ± 13.6 vs. 71.3 ± 10.3 ms) were significantly longer in the diabetic group than in the control group, indicating increased heterogeneity of ventricular repolarization in type 2 diabetes. During follow-up of 36 patients in the diabetic group for 787 ± 301 days, HbA1c level decreased to 7.3 ± 1.6%, while BMI did not significantly change. In contrast to HbA1c, QT dispersion (45.8 ± 15.0 ms) and Tpeak-Tend in lead V5 (83.6 ± 10.6 ms) were not significantly reduced during the follow-up period. There was no correlation between the change in HbA1c and the change in QT dispersion or Tpeak-Tend.

Conclusions

Increased heterogeneity of ventricular repolarization in type 2 diabetic patients was not reduced during the relatively short follow-up period despite significantly improved glycemic control.

Electrocardiographic repolarization-related variables as predictors of coronary heart disease death in the women's health initiative study

BACKGROUND

We evaluated 25 repolarization-related ECG variables for the risk of coronary heart disease (CHD) death in 52 994 postmenopausal women from the Women's Health Initiative study.

METHODS AND RESULTS

Hazard ratios from Cox regression were computed for subgroups of women with and without cardiovascular disease (CVD). During the average follow-up of 16.9 years, 941 CHD deaths occurred. Based on electrophysiological considerations, 2 sets of ECG variables with low correlations were considered as candidates for independent predictors of CHD death: Set 1, Ѳ(Tp|Tref), the spatial angle between T peak (Tp) and normal T reference (Tref) vectors; Ѳ(Tinit|Tterm), the angle between the initial and terminal T vectors; STJ depression in V6 and rate-adjusted QTp interval (QTpa); and Set 2, TaVR and TV1 amplitudes, heart rate, and QRS duration. Strong independent predictors with over 2-fold increased risk for CHD death in women with and without CVD were Ѳ(Tp|Tref) >42° from Set 1 and TaVR amplitude >-100 μV from Set 2. The risk for these CHD death predictors remained significant after multivariable adjustment for demographic/clinical factors. Other significant predictors for CHD death in fully adjusted risk models were Ѳ(Tinit|Tterm) >30°, TV1 >175 μV, and QRS duration >100 ms.

CONCLUSIONS

Ѳ(Tp|Tref) angle and TaVR amplitude are associated with CHD mortality in postmenopausal women. The use of these measures to identify high-risk women for further diagnostic evaluation or more intense preventive intervention warrants further study.

CLINICAL TRIAL REGISTRATION URL

http://www.clinicaltrials.gov. Unique identifier: NCT00000611.

Diurnal modulation and sources of variation affecting ventricular repolarization in Warmblood horses

OBJECTIVES

Irregularities in cardiac repolarization are known to predispose for arrhythmias and sudden cardiac death in humans. The QT interval is a quantitative measurement of repolarization, and clinically, the QTc (QT interval corrected for heart rate) and Tpeak to Tend intervals (TpTe) are used as repolarization markers. To support the use of these markers in horses, we sought to describe the possible influence of the environment, time of day, day-to-day effects, T wave conformation, age, body weight (BW), and horse-to-horse variation on repolarization measurements.

ANIMALS

12 Warmblood geldings, age 10.8 ± 4.8 years.

METHODS

Holter ECGs were performed on days 0, 7 and 14. Measures of RR, QT, QTp, QTc and TpTe intervals and T wave conformation were obtained each hour during the recordings. An ANCOVA analysis was performed to estimate diurnal variation and the sources of variation affecting these intervals.

RESULTS

Differences between individual horses were the largest source of repolarization variability although the environment had a significant effect on repolarization as well. Diurnal variation affected both the RR interval and the repolarization markers. The QT, QTc and TpTe intervals were prolonged on day 0. Biphasic T waves shortened the TpTe interval approximately 10 ms. Age and BW did not appear to affect repolarization.

CONCLUSIONS

Equine repolarization markers exhibit significant variation. Factors affecting repolarization measurements include horse-to-horse variation, diurnal variation, the environment, and T wave conformation. These factors must be considered if markers of equine repolarization are used diagnostically.

Abnormal repolarization in the acute myocardial infarction patients: a frequency-based characterization

Despite ST elevation having poor sensitivity for acute myocardial infarction (AMI), it remains the main electrocardiographic (ECG) repolarization index for AMI diagnosis. Aim of the present study was to propose a new f99 index, defined as the frequency at which the repolarization normalized cumulative energy reaches 99%, for ECG AMI discrimination from health with good sensitivity and good specificity. Evaluation of such f99 index was performed on 12-standard-lead (I, II, III, aV1, aVr, aVf, V1 to V6) ECG recordings of 47 healthy controls and 108 acute myocardial infarction (AMI) patients. Repolarization dispersion caused f99 distributions to be significantly lead dependent. In most leads (leads I, II, aVl, aVr, V2-V6), f99 median value was lower in the healthy controls (10-17 Hz) than in the AMI patients (12-38 Hz) indicating higher frequency components (i.e. a more fragmented repolarization) in the latter population. AMI patients from healthy controls discrimination by f99, evaluated in terms of sensitivity (Se) and specificity (Sp), was also lead dependent. Single-lead analysis indicated leads I (Se=80%, Sp=77%) and aVl (Se=84%, Sp=74%) as optimal. Instead, lead-system analysis, performed to overcome dispersion issues, provided the best results when averaging over the 6 precordial leads (Se= 81% and Sp=74%). In conclusion, our new f99 index appears as a promising tool for non-invasively and reliably discriminate AMI patients from healthy subjects.

Changes in QTc interval in the citalopram for agitation in Alzheimer's disease (CitAD) randomized trial

Background

A Food and Drug Administration (FDA) safety communication in August 2011 warned that citalopram was associated with a dose dependent risk of QT prolongation and recommended dose restriction in patients over the age of 60 but did not provide data for this age group.

Methods

CitAD was a randomized, double-masked, placebo-controlled, multicenter clinical trial for agitation in Alzheimer's disease (AD). Participants were assigned to citalopram (target dose of 30 mg/day) or placebo in a 1∶1 ratio. 186 people, 181 of whom were over the age of 60, having probable AD with clinically significant agitation were recruited from September 2009 to January 2013. After the FDA safety communication about citalopram, ECG was added to the required study procedures before enrollment and repeated at week 3 to monitor change in QTc interval. Forty-eight participants were enrolled after enhanced monitoring began.

Results

Citalopram treatment was associated with a larger increase in QTc interval than placebo (difference in week 3 QTc adjusting for baseline QTc: 18.1 ms [95% CI: 6.1, 30.1]; p = 0.004). More participants in the citalopram group had an increase ≥30 ms from baseline to week 3 (7 in citalopram versus 1 in placebo; Fisher's exact p = 0.046), but only slightly more in the citalopram group met a gender-specific threshold for prolonged QTc (450 ms for males; 470 ms for females) at any point during follow-up (3 in citalopram versus 1 in placebo, Fisher's exact p = 0.611). One of the citalopram participants who developed prolonged QTc also displayed ventricular bigeminy. No participants in either group had a cardiovascular-related death.

Conclusion

Citalopram at 30 mg/day was associated with improvement in agitation in patients with AD but was also associated with QT prolongation.

Trial Registration

ClinicalTrials.gov NCT00898807

Cardiac potassium channel subtypes: new roles in repolarization and arrhythmia

About 10 distinct potassium channels in the heart are involved in shaping the action potential. Some of the K+ channels are primarily responsible for early repolarization, whereas others drive late repolarization and still others are open throughout the cardiac cycle. Three main K+ channels drive the late repolarization of the ventricle with some redundancy, and in atria this repolarization reserve is supplemented by the fairly atrial-specific KV1.5, Kir3, KCa, and K2P channels. The role of the latter two subtypes in atria is currently being clarified, and several findings indicate that they could constitute targets for new pharmacological treatment of atrial fibrillation. The interplay between the different K+ channel subtypes in both atria and ventricle is dynamic, and a significant up- and downregulation occurs in disease states such as atrial fibrillation or heart failure. The underlying posttranscriptional and posttranslational remodeling of the individual K+ channels changes their activity and significance relative to each other, and they must be viewed together to understand their role in keeping a stable heart rhythm, also under menacing conditions like attacks of reentry arrhythmia.

Heart rate-corrected QT interval is an independent predictor of all-cause and cardiovascular mortality in individuals with type 2 diabetes: the Diabetes Heart Study

OBJECTIVE

Heart rate-corrected QT (QTc) interval is associated with mortality in the general population, but this association is less clear in individuals with type 2 diabetes. We assessed the association of QTc interval with all-cause and cardiovascular disease (CVD) mortality in the Diabetes Heart Study.

RESEARCH DESIGN AND METHODS

We studied 1,020 participants with type 2 diabetes (83% European Americans; 55% women; mean age 61.4 years) who were free of atrial fibrillation, major ventricular conduction defects, and antiarrhythmic therapy at baseline. QT duration was automatically calculated from a standard 12-lead electrocardiogram (ECG). Following American Heart Association/American College of Cardiology Foundation recommendations, a linear scale was used to correct the QT for heart rate. Using Cox regression, risk was estimated per 1-SD increase in QTc interval as well as prolonged QTc interval (>450 ms) vs. normal QTc interval for mortality.

RESULTS

At baseline, the mean (SD) QTc duration was 414.9 ms (18.1), and 3.0% of participants had prolonged QTc. After a median follow-up time of 8.5 years (maximum follow-up time 13.9 years), 204 participants were deceased. In adjusted multivariate models, a 1-SD increase in QTc interval was associated with an 18% higher risk for all-cause mortality (hazard ratio 1.18 [95% CI 1.03-1.36]) and 29% increased risk for CVD mortality (1.29 [1.05-1.59]). Similar results were obtained when QTc interval was used as a categorical variable (prolonged vs. normal) (all-cause mortality 1.73 [0.95-3.15]; CVD mortality 2.86 [1.35-6.08]).

CONCLUSIONS

Heart rate QTc interval is an independent predictor of all-cause and CVD mortality in this population with type 2 diabetes, suggesting that additional prognostic information may be available from this simple ECG measure.

Risk prediction of cardiovascular death based on the QTc interval: evaluating age and gender differences in a large primary care population

Aims

Using a large, contemporary primary care population we aimed to provide absolute long-term risks of cardiovascular death (CVD) based on the QTc interval and to test whether the QTc interval is of value in risk prediction of CVD on an individual level.

Methods and results

Digital electrocardiograms from 173 529 primary care patients aged 50–90 years were collected during 2001–11. The Framingham formula was used for heart rate-correction of the QT interval. Data on medication, comorbidity, and outcomes were retrieved from administrative registries. During a median follow-up period of 6.1 years, 6647 persons died from cardiovascular causes. Long-term risks of CVD were estimated for subgroups defined by age, gender, cardiovascular disease, and QTc interval categories. In general, we observed an increased risk of CVD for both very short and long QTc intervals. Prolongation of the QTc interval resulted in the worst prognosis for men whereas in women, a very short QTc interval was equivalent in risk to a borderline prolonged QTc interval. The effect of the QTc interval on the absolute risk of CVD was most pronounced in the elderly and in those with cardiovascular disease whereas the effect was negligible for middle-aged women without cardiovascular disease. The most important improvement in prediction accuracy was noted for women aged 70–90 years. In this subgroup, a total of 9.5% were reclassified (7.2% more accurately vs. 2.3% more inaccurately) within clinically relevant 5-year risk groups when the QTc interval was added to a conventional risk model for CVD.

Conclusion

Important differences were observed across subgroups when the absolute long-term risk of CVD was estimated based on QTc interval duration. The accuracy of the personalized CVD prognosis can be improved when the QTc interval is introduced to a conventional risk model for CVD.

Short-term repeatability of electrocardiographic Tpeak-Tend and QT intervals

BACKGROUND

The electrocardiographic (ECG) Tpeak-Tend interval (TpTe) is associated with arrhythmias and sudden cardiac death. TpTe offers a supplementary measure for the QT interval (QT), yet its repeatability has not been established.

PURPOSE

Evaluate short-term repeatability of TpTe and QT.

METHODS

Four ECGs were obtained on sixty participants. The sources of variation, intra-class correlation coefficient (ICC) - an index of reproducibility - and minimal detectable change (MDC) were estimated for TpTe and QT. The impact of repeated measurements on repeatability was estimated for a hypothetical clinical trial designed to detect drug-induced prolongation of TpTe and QT.

RESULTS

We used heart rate-adjusted QT [(QT)a] but TpTe in the study group was rate-invariant. The ICC [95% confidence interval (CI)] was 0.77 (0.69, 0.85) for TpTe, 0.75 (0.65, 0.85) for QT and 0.60 (0.47, 0.73) for (QT)a. The MDC (ms) was 21, 32 and 26 for TpTe, QT and (QT)a respectively.

CONCLUSION

TpTe has excellent repeatability supporting its use as a supplement to QT in observational and clinical studies.

Drug-gene interactions and the search for missing heritability: a cross-sectional pharmacogenomics study of the QT interval

Variability in response to drug use is common and heritable, suggesting that genome-wide pharmacogenomics studies may help explain the 'missing heritability' of complex traits. Here, we describe four independent analyses in 33 781 participants of European ancestry from 10 cohorts that were designed to identify genetic variants modifying the effects of drugs on QT interval duration (QT). Each analysis cross-sectionally examined four therapeutic classes: thiazide diuretics (prevalence of use=13.0%), tri/tetracyclic antidepressants (2.6%), sulfonylurea hypoglycemic agents (2.9%) and QT-prolonging drugs as classified by the University of Arizona Center for Education and Research on Therapeutics (4.4%). Drug-gene interactions were estimated using covariable-adjusted linear regression and results were combined with fixed-effects meta-analysis. Although drug-single-nucleotide polymorphism (SNP) interactions were biologically plausible and variables were well-measured, findings from the four cross-sectional meta-analyses were null (Pinteraction>5.0 × 10(-8)). Simulations suggested that additional efforts, including longitudinal modeling to increase statistical power, are likely needed to identify potentially important pharmacogenomic effects.

Comparison of automated measurements of electrocardiographic intervals and durations by computer-based algorithms of digital electrocardiographs

BACKGROUND AND PURPOSE

Automated measurements of electrocardiographic (ECG) intervals are widely used by clinicians for individual patient diagnosis and by investigators in population studies. We examined whether clinically significant systematic differences exist in ECG intervals measured by current generation digital electrocardiographs from different manufacturers and whether differences, if present, are dependent on the degree of abnormality of the selected ECGs.

METHODS

Measurements of RR interval, PR interval, QRS duration, and QT interval were made blindly by 4 major manufacturers of digital electrocardiographs used in the United States from 600 XML files of ECG tracings stored in the US FDA ECG warehouse and released for the purpose of this study by the Cardiac Safety Research Consortium. Included were 3 groups based on expected QT interval and degree of repolarization abnormality, comprising 200 ECGs each from (1) placebo or baseline study period in normal subjects during thorough QT studies, (2) peak moxifloxacin effect in otherwise normal subjects during thorough QT studies, and (3) patients with genotyped variants of congenital long QT syndrome (LQTS).

RESULTS

Differences of means between manufacturers were generally small in the normal and moxifloxacin subjects, but in the LQTS patients, differences of means ranged from 2.0 to 14.0 ms for QRS duration and from 0.8 to 18.1 ms for the QT interval. Mean absolute differences between algorithms were similar for QRS duration and QT intervals in the normal and in the moxifloxacin subjects (mean ≤6 ms) but were significantly larger in patients with LQTS.

CONCLUSIONS

Small but statistically significant group differences in mean interval and duration measurements and means of individual absolute differences exist among automated algorithms of widely used, current generation digital electrocardiographs. Measurement differences, including QRS duration and the QT interval, are greatest for the most abnormal ECGs.

Use of the dominant T wave to enhance reliability of T-wave offset identification

T-wave offset (Toff) identification may be jeopardized by the presence of a significant inter-method (IMV) and inter-lead (ILV) Toff variability. Thus, the aim of the present study was to investigate if the dominant T wave (DTW) may be used to enhance Toff-identification reliability. DTWs and 15-lead ECG T waves of 46 control healthy subjects (CHS) and 103 acute myocardial infarction patients (AMIP) were analyzed for Toff identification using Zhang et al.'s (M1) and Daskalov and Christov's (M2) methods. Results indicate that IMV is significantly reduced when identifying Toff from the DTW rather than from single ECG leads in both populations (CHS: 5ms vs. 5-15ms; AMIP: 10ms vs. 10-20ms). Moreover, when analyzing ILV, Toff was found to be equivalent (correlation=0.71-0.98; P<10(-14)) to the median Toff among leads, but required only one identification instead of 15. Thus, the DTW can be used to enhance Toff-identification reliability.

No association between high-density lipoprotein levels and ventricular repolarization indexes in subjects with primary hypercholesterolemia

OBJECTIVE

Data regarding the effect of lipid parameters on repolarization are sparse. Recent data indicate that reconstituted HDL administration shortens repolarization in cardiomyocytes as well as the corrected QT (QTc) interval in human subjects. We investigated the potential association of high-density lipoprotein cholesterol (HDL-C) levels with conventional and novel electrocardiographic markers of ventricular repolarization in patients with hypercholesterolemia.

METHODS

Consecutive subjects with primary hypercholesterolemia were recruited. We recorded clinical and laboratory parameters as well as electrocardiographic indexes. With regard to ventricular repolarization, we calculated the QTc interval, the T peak-to-end (Tpe) interval, and the Tpe/QT ratio.

RESULTS

The study population consisted of 440 patients (199 men) with a median age of 56 [48-65] years. The correlation analysis (Spearman's) failed to show any association between HDL-C and any of the studied electrocardiographic parameter. Moreover, no correlation between other lipid parameters and the electrocardiograhic indexes was evident. Also, a comparison of the ventricular repolarization parameters between different HDL-C quartile groups (HDL-Q1: ≤ 1.11 mmol/L; HDL-Q2: 1.12-1.29 mmol/L; HDL-Q3: 1.30-1.53 mmol/L; HDL-Q4: ≥ 1.54 mmol/L) was performed. Specifically, the differences in QTc (p: 0.372), Tpe in leads II (p: 0.356), V2 (p: 0.372), V5 (p: 0.112), and Tpe/QT in leads II (p: 0.348), V2 (p: 0.162), V5 (p: 0.122) were not significant.

CONCLUSION

HDL-C levels are not associated with the QTc interval or indexes of repolarization dispersion in patients with primary hypercholesterolemia. The potential antiarrhythmic efficacy of HDL should be further evaluated in the setting of myocardial ischemia where dynamic changes in the heterogeneity of ventricular repolarization ensue.

Prolonged QTc interval predicts all-cause mortality in patients with rheumatoid arthritis: an association driven by high inflammatory burden

OBJECTIVE

RA associates with an increased rate of sudden cardiac death (SCD). A prolonged QTc interval has been associated with arrhythmogenic and SCD in patients with long QT syndrome. Despite the previously reported contemporary association of CRP with SCD, thus far no studies have examined the association of QTc with mortality in RA, a condition characterized by high inflammatory burden. The aim of this study was to examine the role of electrocardiography (QT corrected interval) in predicting all-cause mortality in patients with RA who have an increased rate of SCD and a high inflammatory burden.

METHODS

Three hundred and fifty-seven RA patients with detailed baseline clinical characterization and 12-lead ECGs were followed up for a mean of 73.0 (S.D. 18.3) months. Linear and Cox regression analyses were used to identify variables that associate with QTc and examine its association with all-cause mortality.

RESULTS

The patients' mean age was 60.6 (S.D. 12.0) years, 267 (74.8%) were females and 54 (15.1%) died during the follow-up period. Age (β = 0.231, P < 0.001), gender (β = 0.137, P = 0.008) and CRP (β = 0.144, P = 0.006) associated independently with QTc in RA patients. The crude hazard ratio (HR) for total mortality per 50-ms increase in QTc was 2.17 (95% CI 1.21, 3.90). This association remained significant [HR = 2.18 (95% CI 1.09, 4.35)] after adjustment for identified confounders (cardiovascular and RA specific), but was lost [HR = 1.73 (95% CI 0.83, 3.62)] when CRP was included in the model.

CONCLUSION

A 50-ms increase in QTc interval associates with a doubling of the hazard for all-cause mortality in patients with RA. The observed contemporary association of QTc with CRP levels indicates a potentially hazardous interplay between inflammation and arrhythmogenesis. Future studies are needed to confirm the above findings and explore underlying mechanisms.

Interictal 12-lead electrocardiography in patients with epilepsy

Interictal electrocardiographic predictors of sudden unexpected death in epilepsy (SUDEP) are unknown. This study was designed to identify the unique features of the interictal 12-lead electrocardiogram (EKG) in patients with epileptic seizures. We conducted a retrospective chart review of adult patients below the age of 65 admitted to our epilepsy monitoring unit. Using EEG telemetry data, we classified patients as having nonepileptic seizures (NESs), probable epilepsy (PE), or definite epilepsy (DE) and analyzed 12-lead EKGs obtained on admission. Patients with NESs were assigned as the control group. We included patients taking antipsychotic and/or antidepressant medications but excluded patients with medical conditions or taking other medications that would otherwise confound EKG measurements. Out of the 1007 charts reviewed, 195 patients were included in our analysis, and extensive subgroup analyses were performed. We found that patients with definite localization-related epilepsy displayed a significantly longer average PR interval (162.1 ms) than patients with NESs (148.8 ms). This effect was pronounced in female patients and did not vary with the number of antiepileptic drugs (AEDs) prescribed. In contrast to previous studies, mean QTc intervals were not significantly different between DE (428 ms) and NESs (422.6 ms). However, within females, this difference reached statistical significance (DE: 434.6 ms, NESs: 424.6 ms). Antiepileptic drug polytherapy was associated with a significantly lower QTc interval (416 ms in patients on 4-6 drugs and 436.4 ms in patients on 0-1 drugs). Levetiracetam was the most commonly used AED and was associated with the longest average PR (163 ms) and QTc (432 ms) intervals. The mean QRS axis displayed a significant leftward shift in patients with localization-related epilepsy (35.6° versus 54.3° in patients with NESs) and also in female patients with DE (42.1° versus 55.4° in female patients with NESs). No differences were observed between patients with left versus right hemisphere seizure foci. Overall, these findings may reflect cardiac structural changes and/or alterations in autonomic tone that deserve closer study. Further, longer-term prospective studies are required to understand how these electrocardiographic signatures may predict sudden unexpected death in epilepsy.

Electrocardiographic predictors of incident heart failure in men and women free from manifest cardiovascular disease (from the Atherosclerosis Risk in Communities [ARIC] study)

The risk of incident hospitalized heart failure (HF) was evaluated for 23 electrocardiographic (ECG) variables in men and women free from cardiovascular disease. The hazard ratios with 95% confidence intervals were determined from Cox regression analysis for 13,428 participants 45 to 65 years old in the Atherosclerosis Risk in Communities (ARIC) study. New-onset HF during a 14-year follow-up period occurred in 695 men (11.9%) and 721 women (9.5%). Several ECG variables were significant predictors of incident HF when evaluated as single ECG variables. Predominant among them were spatial angles, reflecting deviations of the direction of the repolarization sequence from the normal reference direction. After controlling for collinearity among the ECG variables, the spatial angle between T peak and normal T reference vectors, Ө(Tp|Tref), was a significant independent predictor in men (HF risk increased 31%) and women (HF risk increased 46%). Other independent predictors in men included epicardial repolarization time (62% increased risk) and T wave peak to T wave end (TpTe) interval, reflecting global dispersion of repolarization (27% increased risk). The independent predictors in women, in addition to Ө(Tp|Tref), were Ө(R|STT) the spatial angle between the mean QRS and STT vectors (54% increased risk) and QRS nondipolar voltage (46% increased risk). In conclusion, wide Ө(Tp|Tref), wide Ө(R|STT), and increased QRS nondipolar voltage in women and wide Ө(Tp|Tref), increased epicardial repolarization time, prolonged TpTe interval and T wave complexity in men were independent predictors of incident HF, and the presence of these abnormal findings could warrant additional diagnostic evaluation for possible preventive action for HF.

Electrocardiogram as a screening tool in the general population: a strategic review

Sudden cardiac death (SCD) is a major public health concern, accounting for 400,000 deaths in the US each year. Clinical and autopsy studies have consistently demonstrated a predominant, common pathophysiology in Western populations, showing that the most common electrophysiological mechanism of SCD is ventricular fibrillation, and the most common pathologic substrate is coronary heart disease (CHD). In about half of SCD cases, death is the first clinical manifestation of CHD. Yet risk factors of SCD early in the natural history of conditions predisposing SCD have not been fully identified, and SCD risk stratification strategy in the general population has not been developed. ECG is an easily available, non-expensive and non-invasive tool, which carries valuable information on electrophysiological properties of the heart. However, traditional analysis of ECG includes very limited assessment of the arrhythmogenic substrate. In this review rationale for development of ECG SCD risk score for screening in the general population is discussed.

Normal standards for computer-ECG programs for prognostically and diagnostically important ECG variables derived from a large ethnically diverse female cohort: the Women's Health Initiative (WHI)

BACKGROUND

Substantial new information has emerged recently about the prognostic value for a variety of new ECG variables. The objective of the present study was to establish reference standards for these novel risk predictors in a large, ethnically diverse cohort of healthy women from the Women's Health Initiative (WHI) study.

METHODS AND RESULTS

The study population consisted of 36,299 healthy women. Racial differences in rate-adjusted QT end (QT(ea)) and QT peak (QT(pa)) intervals as linear functions of RR were small, leading to the conclusion that 450 and 390 ms are applicable as thresholds for prolonged and shortened QT(ea) and similarly, 365 and 295 ms for prolonged and shortened QT(pa), respectively. As a threshold for increased dispersion of global repolarization (T(peak)T(end) interval), 110 ms was established for white and Hispanic women and 120 ms for African-American and Asian women. ST elevation and depression values for the monitoring leads of each person with limb electrodes at Mason-Likar positions and chest leads at level of V1 and V2 were first computed from standard leads using lead transformation coefficients derived from 892 body surface maps, and subsequently normal standards were determined for the monitoring leads, including vessel-specific bipolar left anterior descending, left circumflex artery and right coronary artery leads. The results support the choice 150 μV as a tentative threshold for abnormal ST-onset elevation for all monitoring leads. Body mass index (BMI) had a profound effect on Cornell voltage and Sokolow-Lyon voltage in all racial groups and their utility for left ventricular hypertrophy classification remains open.

CONCLUSIONS

Common thresholds for all racial groups are applicable for QT(ea), and QT(pa) intervals and ST elevation. Race-specific normal standards are required for many other ECG parameters.

Electrocardiographic predictors of coronary heart disease and sudden cardiac deaths in men and women free from cardiovascular disease in the Atherosclerosis Risk in Communities study

Background

We evaluated predictors of coronary heart disease (CHD) death and sudden cardiac death (SCD) in the Atherosclerosis Risk in Communities (ARIC) study.

Methods and Results

The study population included 13 621 men and women 45 to 65 years of age free from manifest cardiovascular disease at entry. Hazard ratios from Cox regression with 95% confidence intervals were computed for 18 dichotomized repolarization‐related ECG variables. The average follow‐up was 14 years. Independent predictors of CHD death in men were TaVR‐ and rate‐adjusted QTend (QT_ea), with a 2‐fold increased risk for both, and spatial angles between mean QRS and T vectors and between Tpeak (T_p) and normal R reference vectors [θ(R_m|T_m) and θ(T_p|T_ref), respectively], with a >1.5‐fold increased risk for both. In women, independent predictors of the risk of CHD death were θ(R_m|T_m), with a 2‐fold increased risk for θ(R_m|T_m), and θ(T_p|T_ref), with a 1.7‐fold increased risk. Independent predictors of SCD in men were θ(T_p|T_ref) and QT_ea, with a 2‐fold increased risk, and θ(T_init|T_term), with a 1.6‐fold increased risk. In women, θ(T_init|T_term) was an independent predictor of SCD, with a >3‐fold increased risk, and θ(R_m|T_m) and TV1 were >2‐fold for both.

Conclusions

θ(R_m|T_m) and θ(T_p|T_ref), reflecting different aspects of ventricular repolarization, were independent predictors of CHD death and SCD, and TaVR and TV1 were also independent predictors. The risk levels for independent predictors for both CHD death and SCD were stronger in women than in men, and QT_ea was a significant predictor in men but not in women.

Institution-wide QT alert system identifies patients with a high risk of mortality

OBJECTIVES

To determine the phenotype and outcome of patients with QTc of at least 500 ms and to create a pro-QTc risk score for mortality.

PATIENTS AND METHODS

An institution-wide computer-based QT alert system was developed and implemented at Mayo Clinic in Rochester, Minnesota. This system screens all electrocardiograms (ECGs) performed and alerts the physician if the QTc is 500 ms or greater. Between November 10, 2010, and June 30, 2011, 86,107 ECGs were performed in 52,579 patients. Clinical diagnoses, laboratory abnormalities, and medications known to influence the QT interval were collected from the medical records and summarized in a new pro-QTc score. Survival was compared with that of the 51,434 Mayo Clinic patients with a QTc less than 500 ms during the same period.

RESULTS

QT alerts were sent for 1145 patients (2%); of these, 470 (41%) had no other identifiable ECG reason for QT prolongation (eg, pacing). All-cause mortality during a mean ± SD of 224 ± 174 days of follow-up was 19% in those with QTc of 500 ms or greater compared with 5% in patients with QTc less than 500 ms (log-rank P<.001). The pro-QTc score was an age-independent predictor of mortality (pro-QTc score: hazard ratio, 1.18; 95% CI, 1.05-1.32; P=.006; age: hazard ratio, 1.02; 95% CI, 1.01-1.03; P=.004.). QT-prolonging medications accounted for 37% of the pro-QTc score.

CONCLUSION

This novel institution-wide QT alert system identified patients with a high risk of mortality. The pro-QTc score, reflecting patients' multimorbidity and multipharmacy, was an independent predictor of mortality. The QT alert system may increase a physician's awareness of a high-risk patient. Potentially lifesaving interventions can be facilitated by reducing the modifiable factors of the pro-QTc score.

Normal electrocardiographic QT interval in race-fit Standardbred horses at rest and its rate dependence during exercise

OBJECTIVES

Cardiac repolarization, measured as QT and Tpeak to Tend (TpTe) intervals on the ECG, is important, as irregularities caused by diseases, ventricular hypertrophy, drugs and genetic defects can trigger arrhythmias which predispose human patients to syncope and sudden cardiac death. In horses, repolarization is not well described and therefore QT analysis cannot yet be used diagnostically. Therefore, we sought to describe reference values for the normal QT and TpTe intervals in Standardbreds and to determine the best method for heart rate (HR) correction.

ANIMALS

30 Standardbreds.

METHODS

QT and TpTe intervals were measured during rest and exercise and plotted against HR converted to Rpeak to Rpeak interval (RR). Data were fitted with relevant regression models. Intra- and inter-observer agreement was assessed using Bland-Altman analyses.

RESULTS

Data were best described by a piecewise linear model (r(2) > 0.97). Average prediction error of this model was smaller than for both Bazett and Fridericia corrections. Coefficient of repeatability of intra- and inter-observer variability was 8.76 ms and 5.64 ms respectively and coefficient of variation was 1.77% and 2.76% respectively. TpTe increased with RR in stallions.

CONCLUSIONS

The QT interval in Standardbred horses shortens with decreasing RR interval (increasing HR) as in humans, but in a markedly different order as it clearly follows a piecewise linear model. The equine QT interval can be measured easily and there is small intra- and inter-observer variability. This model of the equine QT interval provides clinicians with a method that could support a diagnosis of repolarization disturbances in horses.

Fine-mapping and initial characterization of QT interval loci in African Americans

The QT interval (QT) is heritable and its prolongation is a risk factor for ventricular tachyarrhythmias and sudden death. Most genetic studies of QT have examined European ancestral populations; however, the increased genetic diversity in African Americans provides opportunities to narrow association signals and identify population-specific variants. We therefore evaluated 6,670 SNPs spanning eleven previously identified QT loci in 8,644 African American participants from two Population Architecture using Genomics and Epidemiology (PAGE) studies: the Atherosclerosis Risk in Communities study and Women's Health Initiative Clinical Trial. Of the fifteen known independent QT variants at the eleven previously identified loci, six were significantly associated with QT in African American populations (P≤1.20×10(-4)): ATP1B1, PLN1, KCNQ1, NDRG4, and two NOS1AP independent signals. We also identified three population-specific signals significantly associated with QT in African Americans (P≤1.37×10(-5)): one at NOS1AP and two at ATP1B1. Linkage disequilibrium (LD) patterns in African Americans assisted in narrowing the region likely to contain the functional variants for several loci. For example, African American LD patterns showed that 0 SNPs were in LD with NOS1AP signal rs12143842, compared with European LD patterns that indicated 87 SNPs, which spanned 114.2 Kb, were in LD with rs12143842. Finally, bioinformatic-based characterization of the nine African American signals pointed to functional candidates located exclusively within non-coding regions, including predicted binding sites for transcription factors such as TBX5, which has been implicated in cardiac structure and conductance. In this detailed evaluation of QT loci, we identified several African Americans SNPs that better define the association with QT and successfully narrowed intervals surrounding established loci. These results demonstrate that the same loci influence variation in QT across multiple populations, that novel signals exist in African Americans, and that the SNPs identified as strong candidates for functional evaluation implicate gene regulatory dysfunction in QT prolongation.

Prolongation of QTc and risk of stroke: The REGARDS (REasons for Geographic and Racial Differences in Stroke) study

OBJECTIVES

The purpose of this study was to examine the association between prolongation of QT interval corrected for heart rate (QTc) with incident stroke.

BACKGROUND

Unlike cardiovascular morbidity and mortality, little is known about the relationship between QTc and risk of stroke.

METHODS

A total of 27,411 participants age 45 years and older without previous stroke from the REGARDS (REasons for Geographic and Racial Differences in Stroke) study were included in this analysis. QTc was calculated using Framingham formula (QTc(Fram)). Stroke cases were identified and adjudicated during up to 8.2 years of follow-up (median, 5.1 years).

RESULTS

The risk of incident stroke in study participants with prolonged QTc(Fram) was almost 3 times the risk in those with normal QTc(Fram) (hazard ratio [HR] [95% confidence interval (CI)]: 2.88 [2.12 to 3.92], p < 0.0001). After adjustment for demographics (age, race, and sex), traditional stroke risk factors (antihypertensive medication use, systolic blood pressure, current smoking, diabetes, left ventricular hypertrophy, atrial fibrillation, and previous cardiovascular disease), warfarin use, aspirin use, QRS duration and use of QTc-prolonging drugs, the risk of stroke remained significantly high (HR [95% CI]: 1.67 [1.16 to 2.41], p = 0.0061) and was consistent across several subgroups of REGARDS study participants. Similar results were obtained when the risk of stroke was estimated per 1-SD increase in QTc(Fram), (HR [95% CI]: 1.12 [1.03 to 1.21], p = 0.0053 in multivariable-adjusted model) and when other QTc correction formulas including those of Hodge, Bazett, and Fridericia were used.

CONCLUSIONS

QTc prolongation is associated with a significantly increased risk of incident stroke independent of traditional stroke risk factors. Examining the risk of stroke associated with QTc-prolonging drugs may be warranted.